Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    Super-performance in a palm species
    Jansen, Merel - \ 2016
    Wageningen University. Promotor(en): Niels Anten; Pieter Zuidema, co-promotor(en): Frans Bongers; M. Martínez-Ramos. - Wageningen : Wageningen University - ISBN 9789462579996 - 193
    chamaedorea elegans - understorey - tropical forests - spatial variation - leaves - growth - population ecology - defoliation - genetic variation - chamaedorea elegans - onderlaag - tropische bossen - ruimtelijke variatie - bladeren - groei - populatie-ecologie - ontbladering - genetische variatie

    The world is changing rapidly due to anthropogenic disturbance. Effects include: global warming, massive pollution, a changed global nitrogen cycle, high rates of land-use change, and exotic species spread. This has a tremendous impact on both natural and agricultural systems. To understand these impacts, good understanding of ecological systems and underlying drivers is necessary. Ecological systems can be studied at different levels of aggregation. Different levels of aggregation influence each other and are also influenced by external drivers like the environment. The population level is of particular interest, because many important ecological processes occur at the population level, like evolution, extinction, and invasion. Ecologists are increasingly recognizing that population processes are strongly influenced by one level of aggregation lower, the individual level. Individual heterogeneity (i.e. differences between individuals in performance), determines many population processes including population growth rate. However, the exact relations between individual heterogeneity, the external drivers of it, and the population level are not always well understood. Furthermore, methods to analyze these relations are not always available.

    Individual heterogeneity occurs at different temporal scales, ranging from short- to long-term performance differences between individuals, where short- and long-term refer to the expected lifespan of the species in question. Short-term differences between individuals are relatively easily identifiable and are common in almost all species. But long-term differences are much harder to determine especially for long-lived organisms. Long-term differences between individuals in reproduction have been identified for several animal species, and in growth for several tree species, but less is known about the existence of such differences in other life forms (e.g. palms, lianas or clonal plants). Quantifying the extent to which individuals differ is essential for understanding the influence of individual heterogeneity on population processes. Super-performing individuals (i.e. individuals that persistently grow faster and reproduce more than others), probably contribute more to the growth of the population and therefore to future generations. Future populations will, therefore, have the genetic characteristics of the super-performers. Which characteristics this will be, depends on the genetic and environmental drivers of super-performance. Full understanding of the influence of individual heterogeneity on population processes, therefore, requires knowledge of the underlying causes of individual heterogeneity.

    For many species, it is known that spatial variation in environmental conditions can cause short-term performance differences between individuals, but it is often not clear if the same environmental factors that cause short-term performance differences are also the environmental factors that cause long-term performance differences. Furthermore, genetic variation is known to cause performance differences, but to what extent is not well studied in natural long-lived plant populations. Within-population genetic variation can be maintained in habitats that are characterized by strong temporal or spatial heterogeneity in environmental conditions if the performance of a genotype relative to others depends on the environment it experiences.

    Super-performing individuals possibly play an important role in the resistance and resilience of populations to disturbance (i.e. maintaining and recovering population growth rate under stress), because super-performers potentially contribute more to the recovery of the population. However, this depends on the relative tolerance to disturbance of super-performers compared to under-performers. A positive relation between performance and tolerance would make super-performers more important, while a negative relation would make them less important. Many types of disturbances entail leaf loss and tolerance to leaf loss is associated with performance being larger than what one would assume based on the amount of leaf area loss. Tolerance can be achieved by compensating for leaf loss in terms of growth rate, which entails either allocating more new assimilates to leaves, allocating new assimilates more efficiently to leaf area (i.e. by increasing specific leaf area), or growing faster with existing leaf area (i.e. by increasing net assimilation rate). Genetic variation in tolerance and compensatory responses would allow populations to adapt to changes in disturbance events that entail leaf loss.

    Individual heterogeneity could also have implications for management. Plant and animal populations are managed at many different levels ranging from harvest from natural populations to modern agricultural practices. When harvesting from natural populations, it might be beneficial to spare the individuals that are most important for future production. Individuals could be spared, either because they contribute most to population growth, because they are tolerant to harvesting (which is relevant when only part of a plant is harvested), or when they start producing less or lower quality product. The productivity of natural populations could also be increased by actively promoting those environmental conditions and genotypes that allow for high productivity, which is the basis of agriculture and common practice in forest management. To determine how this can best be done, knowledge of the causes of individual heterogeneity is necessary.

    The general aim of this thesis is to identify and quantify the mechanisms that determine individual heterogeneity and to determine how this heterogeneity, in turn, affects population level processes. This aim was divided into four main questions that I addressed: (1) To what extent do individuals differ in performance? (2) What causes individual heterogeneity in performance? (3) What are the demographic consequences of individual heterogeneity? (4) Can individual differences be used to improve the management of populations? To answer these questions, we used the tropical forest understorey palm Chamaedorea elegans as a study system, of which the leaves are an important non-timber forest product that is being used in the floral industry worldwide. We collected demographic data, measured spatial variation in environmental conditions, and applied a defoliation treatment to simulate leaf harvesting, in a natural population in Chiapas, Mexico. Furthermore, we grew seedlings from different mothers from our study population in the greenhouses of Wageningen University, where we also applied a defoliation treatment.

    In Chapter 2 we quantified the extent to which individuals differ in long-term growth rate, and analyzed the importance of fast growers for population growth. We reconstructed growth histories from internodes and showed that growth differences between individuals are very large and persistent in our study population. This led to large variation in life growth trajectories, with individuals of the same age varying strongly in size. This shows that not only in canopy trees but also in species in the light limited understorey growth differences can be very large. Past growth rate was found to be a very good predictor of current performance (i.e. growth and reproduction). Using an Integral Projection Model (i.e. a type of demographic model) that was based on size and past growth rate, we showed that fast-growing individuals are much more important for population growth than others: the 50% fastest growing individuals contributed almost two times as much to population growth as the 50% slowest growing individuals.

    In Chapter 3 we analyzed the extent to which observed long-term growth differences can be caused by environmental heterogeneity. Short-term variation in performance was mainly driven by light availability, while soil variables and leaf damage had smaller effects, and spatial heterogeneity in light availability and soil pH were autocorrelated over time. Using individual-based simulation models, we analyzed the extent to which spatial environmental heterogeneity could explain observed long-term variation in growth, and showed that this could largely be explained if the temporal persistence of light availability and soil pH was taken into account. We also estimated long-term inter-individual variation in reproduction to be very large. We further analyzed the importance of temporal persistence in environmental variation for long-term performance differences, by analyzing the whole range of values of environmental persistence, and the strength of the effect of the environmental heterogeneity on short-term performance. We showed that long-term performance differences become large when either the strength of the effect of the environmental factor on short-term performance is large, or when the spatial variation in the environmental factor is persistent over time. This shows that an environmental factor that in a short-term study might have been dismissed as unimportant for long-term performance variation, might, in reality, contribute strongly.

    In Chapter 4 we tested for genetic variation in growth potential, tolerance to leaf loss, compensatory growth responses, and if growth potential and tolerance were genetically correlated in our study population. We quantified compensatory responses with an iterative growth model that takes into account the timing of leaf loss. Genetic variation in growth potential was large, and plants compensated strongly for leaf loss, but genetic variation in tolerance and compensatory growth responses was very limited. Growth performances in defoliated and undefoliated conditions were positively genetically correlated (i.e. the same genotypes perform relatively well compared to others, both with and without the stress of leaf loss). The high genetic variation in growth potential and the positive correlation between treatments suggests that the existence of super-performing individuals in our study population likely has (at least in part) a genetic basis. These super-performing individuals, that grow fast even under the stress of leaf loss, possibly contribute disproportionately to population resistance and resilience to disturbance. The low genetic variation in tolerance and compensatory responses, however, suggests that populations might have limited ability to adapt to changes in disturbance regimes that entail increases in leaf loss. Furthermore, the high genetic variation in growth potential could potentially be used in management practices like enrichment planting.

    In Chapter 5 we explore the potential of using individual heterogeneity to design smarter harvest schemes, by sparing individuals that contribute most to future productivity. We tested if fast and slow growers, and small and large individuals, responded differently to leaf loss in terms of vital rates, but found only very limited evidence for this. Using Integral Projection Models that were based on stem length and past growth rate, we simulated leaf harvest over a period of 20 years, in several scenarios of sparing individuals, which we compared to “Business as usual” (i.e. no individuals being spared, BAU). Sparing individuals that are most important for population growth, was beneficial for population size (and could, therefore, reduce extinction risk), increased annual leaf harvest at the end of the simulation period, but cumulated leaf harvest over 20 years was much lower compared to BAU. Sparing individuals that produced leaves of non-commercial size (i.e. <25cm), therefore allowing them to recover, also resulted in a lower total leaf harvest over 20 years. However, a much higher harvest (a three-fold increase) was found when only leaves of commercial size were considered. These results show that it is possible to increase yield quality and sustainability (in terms of population size) of harvesting practices, by making use of individual heterogeneity. The analytical and modeling methods that we present are applicable to any natural system from which either whole individuals, or parts of individuals, are harvested, and provide an extra tool that could be considered by managers and harvest practitioners to optimize harvest practices.

    In conclusion, in this thesis, I showed that in a long-lived understorey palm growth differences are very large and persistent (Chapter 2) and that it is likely that long-term differences in reproduction are also very large (Chapter 3). I also showed that spatial heterogeneity in environmental conditions can to a large extent explain these differences and that when evaluating the environmental drivers of individual heterogeneity, it is important to take the persistence of spatial variation into account (Chapter 3). Individual heterogeneity also is partly genetically determined. I showed that genetic variation in growth potential to be large (Chapter 4), and that fast growers keep on growing fast under the stress of leaf loss (Chapters 4,5). Therefore it is likely that genetic variation contributes to long-term differences between individuals. Genetic variation for tolerance and compensatory responses was estimated to be low (Chapter 4), suggesting that the adaptive potential of our study population to changes in disturbance events that entail leaf loss might be low. I also showed that super-performing individuals are much more important for the growth of the population (Chapter 2) and that individuals that are important for future production could be used to improve the management of natural populations (Chapter 5).

    This study provides improved insight into the extent of individual heterogeneity in a long-lived plant species and its environmental and genetic drivers, and clearly shows the importance of individual heterogeneity and its drivers for population processes and management practices. It also presents methods on how persistent performance differences between individuals can be incorporated into demographic tools, how these can be used to analyze individual contributions to population dynamics, to extrapolate short-term to long–term environmental effects, and to analyze smart harvesting scenarios that take differences between individuals into account. These results indicate that individual heterogeneity, underlying environmental and genetic drivers, and population processes are all related. Therefore, when evaluating the effect of environmental change on population processes, and in the design of management schemes, it is important to keep these relations in mind. The methodological tools that we presented provide a means of doing this.

    Open gewas kan productie vervroegen en energie besparen : Filosoferen over Het Nieuwe Gewas
    Velden, P. van; Gelder, A. de - \ 2015
    Onder Glas 12 (2015)6/7. - p. 14 - 15.
    glastuinbouw - tomaten - groenten - cultuurmethoden - ontbladering - snoeien - gewasproductie - bereikt resultaat - landbouwkundig onderzoek - greenhouse horticulture - tomatoes - vegetables - cultural methods - defoliation - pruning - crop production - achievement - agricultural research
    Heeft een tomatenplant veel blad nodig om tot een goede productie te komen? Dat is de centrale vraag binnen het project Het Nieuwe Gewas. De proef bij Wageningen UR Glastuinbouw geeft een verrassend resultaat, want ‘plantje pesten’ door extra blad weg te snijden geeft iets productieverhoging in plaats van verlaging.
    Sustainable harvesting of non-timber forest products based on ecological and economic criteria
    Hernandez-Barrios, J.C. ; Anten, N.P.R. ; Martinez-Ramos, M. - \ 2015
    Journal of Applied Ecology 52 (2015)2. - ISSN 0021-8901 - p. 389 - 401.
    lacandona rain-forest - understorey palm - extraction systems - defoliation - growth - reproduction - population - impact - leaf - exploitation
    1. Harvesting of highly valuable non-timber forest products (NTFPs) has been considered a win-win strategy where local people profit while conserving forest biodiversity ecosystem services. Nevertheless the sustainability of NTFP harvesting has been debated as the nature of NTFPs harvesting regimes scale of commercialization are highly heterogeneous, few studies have evaluated the cumulative ecological economic effects of such regimes. Here we assessed the medium-term (10 years) sustainability of NTFP harvesting using Chamaedorea palm leaves a major NTFP from Mesoamerica that is highly valued in the international floral industry as a case study. 2. We used an experimental ecological study and an economic assessment to analyse the sustainability of leaf harvesting in C. ernesti-augustii. A 4-year leaf removal experiment was conducted to assess effects of increasing levels of defoliation (0%, 25%, 50%, 75%, 100% leaf removal, biannually) on palm survivorship, leaf production and leaf quality. Results of this experiment were combined with estimations of harvest economic value to make projections of the availability of leaves and profit per unit area. Finally, we determined harvesting regimes that maximize profit while maintaining medium-term viability of exploited populations. 3. Palms tolerated up to 50% chronic defoliation, but higher defoliation levels reduced survivorship, leaf production and leaf quality. In the long term, this 50% defoliation level maximized harvest volume and profit without significantly affecting palm survival and leaf quality. Our results show that harvesters face the dilemma of either maximizing short-term income leading to rapid exhaustion of stocks, or maintaining exploited populations but maximizing income in the long term. 4. Synthesis and applications. Our study shows that intermediate harvesting levels (=50% leaf removal) are needed to achieve long-term sustainability of Chamaedorea palm leaves. Results of this study have an immediate application for the amendment of the official Mexican law, which enables higher harvesting intensities of Chamaedorea leaves, and for the design of sustainable management strategies. Applications of such strategies should consider communitybased management, fair markets, regulating norms, as well as a thorough communication among stakeholders. Key-words: Chamaedorea ernesti-augustii, defoliation, Mexico, plant demography, socioecological sustainability, tropical rain forest
    Sustainable harvesting of non-timber forest products based on ecological and economic criteria
    Hernandez-Barrios, J.C. ; Anten, N.P.R. ; Martinez-Ramos, M. - \ 2014
    Wageningen UR
    plant demography - tropical rainforest - defoliation - socio-ecological sustainability
    Harvesting of highly valuable non-timber forest products (NTFPs) has been considered a win-win strategy where local people profit while conserving forest biodiversity and ecosystem services. Nevertheless the sustainability of NTFP harvesting has been debated as the nature of NTFPs, harvesting regimes, and scale of commercialization are highly heterogeneous and few studies have evaluated the cumulative ecological and economic effects of such regimes. Here, we assessed the medium-term (10 years) sustainability of NTFP harvesting, using Chameadorea palm leaves, a major NTFP from Mesoamerica that is highly valued in the international floral industry, as a case study. We used an experimental ecological study and an economic assessment to analyse the sustainability of leaf harvesting in C. ernesti-augustii. A four-year leaf removal experiment was conducted to assess effects of increasing levels of defoliation (0%, 25%, 50%, 75%, 100% leaf removal, biannually) on palm survivorship, leaf production and leaf quality. Results of this experiment were combined with estimations of harvest economic value to make projections of the availability of leaves and profit per unit area. Finally, we determined harvesting regimes that maximize profit while maintaining medium-term viability of exploited populations. Palms tolerated up to 50% chronic defoliation, but higher defoliation levels reduced survivorship, leaf production, and leaf quality. In the long-term, this 50% defoliation level maximized harvest volume and profit without significantly affecting palm survival and leaf quality. Our results show that harvesters face the dilemma of either maximizing short-term income leading to rapid exhaustion of stocks, or maintaining exploited populations but maximizing income in the long-term. Synthesis and applications. Our study shows that intermediate harvesting levels (≤ 50% leaf removal) are needed to achieve long-term sustainability of Chameadorea palm leaves. Results of this study have an immediate application for the amendment of the official Mexican law, which enables higher harvesting intensities of Chamaedorea leaves, and for the design of sustainable management strategies. Applications of such strategies should consider community-based management, fair markets, regulating norms, as well as a thorough communication among stakeholders.
    Grazing-induced changes in plant–soil feedback alter plant biomass allocation
    Veen, C.F. ; Vries, S. de; Bakker, E.S. ; Putten, W.H. van der; Olff, H. - \ 2014
    Oikos 123 (2014)7. - ISSN 0030-1299 - p. 800 - 806.
    tallgrass prairie - borne pathogens - invasive plant - grassland - herbivores - community - competition - coexistence - defoliation - diversity
    Large vertebrate herbivores, as well as plant–soil feedback interactions are important drivers of plant performance, plant community composition and vegetation dynamics in terrestrial ecosystems. However, it is poorly understood whether and how large vertebrate herbivores and plant–soil feedback effects interact. Here, we study the response of grassland plant species to grazing-induced legacy effects in the soil and we explore whether these plant responses can help us to understand long-term vegetation dynamics in the field. In a greenhouse experiment we tested the response of four grassland plant species, Agrostis capillaris, Festuca rubra, Holcus lanatus and Rumex acetosa, to field-conditioned soils from grazed and ungrazed grassland. We relate these responses to long-term vegetation data from a grassland exclosure experiment in the field. In the greenhouse experiment, we found that total biomass production and biomass allocation to roots was higher in soils from grazed than from ungrazed plots. There were only few relationships between plant production in the greenhouse and the abundance of conspecifics in the field. Spatiotemporal patterns in plant community composition were more stable in grazed than ungrazed grassland plots, but were not related to plant–soil feedbacks effects and biomass allocation patterns. We conclude that grazing-induced soil legacy effects mainly influenced plant biomass allocation patterns, but could not explain altered vegetation dynamics in grazed grasslands. Consequently, the direct effects of grazing on plant community composition (e.g. through modifying light competition or differences in grazing tolerance) appear to overrule indirect effects through changes in plant–soil feedback.
    Genetic differences in root mass of Lolium perenne varieties under field conditions
    Deru, J.G.C. ; Schilder, H. ; Schoot, J.R. van der; Eekeren, N.J.M. van - \ 2014
    Euphytica 199 (2014)1-2. - ISSN 0014-2336 - p. 223 - 232.
    grazing systems - soil - ryegrass - growth - architecture - defoliation - elongation - management - patterns - capture
    Although grasses have dense rooting systems, nutrient uptake and productivity can be increased, and N-leaching reduced, if rooting is further improved. The variation in root mass of 16 varieties of Lolium perenne was studied under field conditions in two experiments on sandy soil in The Netherlands. The chosen varieties differed in genetic and aboveground characteristics such as ploidy, productivity and grass cover. Root dry matter (RDM) was measured in the 0–8, 8–16 and 16–24 cm soil layers. In summary, we found that RDM of perennial ryegrass differed significantly between varieties under field conditions. These differences were not linked to grass yield, which indicates that it is possible to select perennial ryegrass varieties that combine high aboveground productivityIn this experiment, total RDM was not influenced by ploidy but by grass cover type: high grass cover types had higher RDM. Differences in management between the two experiments possibly explain the differences in RDM and in the influence of chosen characteristics on RDM. Considering challenges in the areas of climate change, water availability, pollution and soil degradation, grass varieties with improved root systems could significantly contribute to a more efficient use of nutrients and water, erosion control, soil improvement and carbon sequestration. with high RDM. In the first experiment, which was managed by cutting, diploid varieties had higher RDM than tetraploid varieties. Grand mean RDM in the second experiment, which was managed by cutting as well as grazing, was lower than in the first experiment.
    Optimal leaf area leads to higher production and higher income : Don't prune too many tomato leaves
    Heuvelink, E. ; Kierkels, T. - \ 2014
    In Greenhouses : the international magazine for greenhouse growers 3 (2014)2. - ISSN 2215-0633 - p. 52 - 53.
    glastuinbouw - solanum lycopersicum - plantenontwikkeling - bladoppervlakte - ontbladering - assimilatie - netto-assimilatiesnelheid - groenten - greenhouse horticulture - solanum lycopersicum - plant development - leaf area - defoliation - assimilation - net assimilation rate - vegetables
    Good light interception is the first step to good production. For that you need sufficient leaf area in the greenhouse. But it’s difficult for a grower to determine how much leaf surface area is present. Research is shedding new insight into this aspect.
    Above- and below-ground herbivory effects on below- ground plant-fungus interactions and plant-soil feedback responses
    Bezemer, T.M. ; Putten, W.H. van der; Martens, H. ; Voorde, T.F.J. van de; Mulder, P.P.J. ; Kostenko, O. - \ 2013
    Journal of Ecology 101 (2013)2. - ISSN 0022-0477 - p. 325 - 333.
    pyrrolizidine alkaloids - senecio-jacobaea - grassland - community - growth - defoliation - allocation - resistance - diversity
    1.Feeding by insect herbivores can affect plant growth and the concentration of defense compounds in plant tissues. Since plants provide resources for soil organisms, herbivory can also influence the composition of the soil community via its effects on the plant. Soil organisms, in turn, are important for plant growth. We tested whether insect herbivores, via their effects on the soil microbial community, can influence plant-soil feedbacks. 2.We first examined the effects of above-ground (AG) and below-ground (B) insect herbivory on the composition of pyrrolizidine alkaloids (PAs) in roots and on soil fungi in roots and rhizosphere soil of ragwort (Jacobaea vulgaris). The composition of fungal communities in roots and rhizosphere soil was affected by both AG and BG herbivory, but fungal composition also differed considerably between roots and rhizosphere soil. The composition of PAs in roots was affected only by BG herbivory. 3.Thirteen different fungal species were detected in roots and rhizosphere soil. The presence of the potentially pathogenic fungus Fusarium oxysporum decreased and that of Phoma exigua increased in presence of BG herbivory, but only in soil samples. 4.We then grew new plants in the soils conditioned by plants exposed to the herbivore treatments and in unconditioned soil. A subset of the new plants was exposed to foliar insect herbivory. Plant-soil feedback was strongly negative, but the feedback effect was least negative in soil conditioned by plants that had been exposed to BG herbivory. There was a negative direct effect of foliar herbivory on plant biomass during the feedback phase, but this effect was far less strong when the soil was conditioned by plants exposed to AG herbivory. AG herbivory during the conditioning phase also caused a soil feedback effect on the PA concentration in the foliage of ragwort. 5.Synthesis. Our results illustrate how insect herbivory can affect interactions between plants and soil organisms, and via these effects how herbivory can alter the performance of late-growing plants. Plant-soil feedback is emerging as an important theme in ecology and these results highlight that plant-soil feedback should be considered from a multitrophic AG and BG perspective
    Herbaceous production in South India-limiting factors and implications for large herbivores
    Ahrestani, F.S. ; Heitkonig, I.M.A. ; Prins, H.H.T. - \ 2011
    Plant and Soil 349 (2011)1-2. - ISSN 0032-079X - p. 319 - 330.
    net primary productivity - nairobi-national-park - tropical grassland - seasonal-variation - plant phenology - savanna - nitrogen - rainfall - defoliation - diversity
    This study's goal was to better understand the growth pattern and limitations of the herbaceous production that supports South India's rich large herbivore grazer assemblage. We conducted a fully factorial nitrogen and water (three levels each) treatment field experiment in the herbivore rich South Indian Western Ghats region to determine the seasonal pattern and the extent to which nitrogen and water availability limit herbaceous production. Graminoid production was found to be nitrogen limited. Despite low rainfall, additional water did not significantly increase overall biomass production nor extend growth in the dry season. Accumulated standing biomass was highest in the late wet season (November) and lowest in the dry season (May). Leaf nitrogen was highest in the early wet season (June) and lowest in the late dry season (March). Grazing had a positive effect on grass production by extending the growing season. Biomass production and graminoid leaf nitrogen concentration levels in the study area were similar to other tropical areas in the world. Also similar to other tropical large herbivore areas, the dry season poses an annual challenge for large herbivores in the study area -particularly the smaller bodied species-to satisfy their nutrient requirements.
    Vertebrate herbivores influence soil nematodes by modifying plant communities
    Veen, C.F. ; Olff, H. ; Duyts, H. ; Putten, W.H. van der - \ 2010
    Ecology 91 (2010)3. - ISSN 0012-9658 - p. 828 - 835.
    below-ground biota - microbial responses - grassland ecosystem - food-web - diversity - vegetation - nitrogen - defoliation - nutrients - patterns
    Abiotic soil properties, plant community composition, and herbivory all have been reported as important factors influencing the composition of soil communities. However, most studies thus far have considered these factors in isolation, whereas they strongly interact in the field. Here, we study how grazing by vertebrate herbivores influences the soil nematode community composition of a floodplain grassland while we account for effects of grazing on plant community composition and abiotic soil properties. Nematodes are the most ubiquitous invertebrates in the soil. They include a variety of feeding types, ranging from microbial feeders to herbivores and carnivores, and they perform key functions in soil food webs. Our hypothesis was that grazing affects nematode community structure and composition through altering plant community structure and composition. Alternatively, we tested whether the effects of grazing may, directly or indirectly, run via changes in soil abiotic properties. We used a long-term field experiment containing plots with and without vertebrate grazers (cattle and rabbits). We compared plant and nematode community structure and composition, as well as a number of key soil abiotic properties, and we applied structural equation modeling to investigate four possible pathways by which grazing may change nematode community composition. Aboveground grazing increased plant species richness and reduced both plant and nematode community heterogeneity. There was a positive relationship between plant and nematode diversity indices. Grazing decreased the number of bacterial-feeding nematodes, indicating that in these grasslands, top-down control of plant production by grazing leads to bottom-up control in the basal part of the bacterial channel of the soil food web. According to the structural equation model, grazing had a strong effect on soil abiotic properties and plant community composition, whereas plant community composition was the main determinant of nematode community composition. Other pathways, which assumed that grazing influenced nematode community composition by inducing changes in soil abiotic properties, did not significantly explain variation in nematode community composition. We conclude that grazing-induced changes in nematode community composition mainly operated via changes in plant community composition. Influences of vertebrate grazers on soil nematodes through modification of abiotic soil properties were of less importance.
    Effect UV-C belichting op myceliumgroei en sporenkieming van Fusarium oxysporum en Fusarium solani: in vitro experimenten
    Wenneker, M. ; Joosten, N.N. - \ 2008
    Zetten : Praktijkonderzoek Plant & Omgeving, Sector Fruit - 20
    glastuinbouw - paprika's - gewassen, groeifasen - ontbladering - gewasbescherming - schimmelbestrijding - fusarium - kwaliteit - teeltsystemen - ziektebestrijdende teeltmaatregelen - greenhouse horticulture - sweet peppers - crop growth stage - defoliation - plant protection - fungus control - fusarium - quality - cropping systems - cultural control
    In dit rapport worden de resultaten beschreven van het onderzoek naar het effect van UV-C belichting op de myceliumgroei en sporenkieming van Fusarium oxysporum en F. solani.
    Spectral and human sensors : hyperspectral remote sensing and participatory GIS for mapping livestock grazing intensity and vegetation in transhumant Mediterranean conservation areas
    Bemigisha, J. - \ 2008
    Wageningen University. Promotor(en): Andrew Skidmore; Herbert Prins, co-promotor(en): Sip van Wieren. - [S.l.] : S.n. - ISBN 9789085049364 - 156
    geografische informatiesystemen - remote sensing - beweidingsintensiteit - cartografie - middellandse-zeegebied - vegetatie - ontbladering - mediterrane graslanden - geographical information systems - remote sensing - grazing intensity - mapping - mediterranean region - vegetation - defoliation - mediterranean grasslands
    Increasing shortage of pasture resources due to land use conversion
    constitutes a major challenge to traditional transhumance systems.
    Reduction of transhumance and related activities leaves the non
    converted areas abandoned. This may lead to change in grazing
    intensity, which might result into change in species composition and
    vegetation pattern. A reduction in grazing intensity might thus
    influence the biodiversity and forage quality of previously more
    intensively grazed areas. Proper management of Mediterranean
    grasslands would require insight on how grazing intensity varies
    across a landscape and how it influences the distribution and
    abundance of plant species.
    The aim of this study was to investigate methods for mapping of
    livestock grazing intensity and vegetation, using hyperspectral remote
    sensing, geographic information systems (GIS) and participatory GIS
    (PGIS). Investigations were undertaken at two main levels. A
    greenhouse experiment was used to investigate the effects of
    defoliation and defoliation time for two species grown in mono and
    mixed culture on the height and dry matter yield as measures of
    regrowth and competitive ability of two livestock forage grasses
    selected from a transhumant Mediterranean area. Narrow band
    hyperspectral reflectance, indices and the red-edge position were
    investigated to see if they may be used to study these effects. At field
    landscape level, we tested the use of local people’s knowledge in
    mapping grazing intensity through the application of PGIS.
    The results from the greenhouse experiment showed that the species
    with higher dry matter yield (Lolium multiflorum) had a significantly
    higher relative regrowth rate and possibly higher competitive ability
    than its competitor Dactylis glomerata (P < 0.05). Increase in dry
    matter yield was shown as the trait that determines competitive
    ability in the early established stage of the two grass species (period
    of 13 to 18 weeks after sowing). The experiment also provided insight
    on the persistence of forage species that are of grazing preference.
    Selective clipping did not alter the competitive ability of D. glomerata
    to surpass that of L. multiflorum when the former was clipped at
    lower clipping intensity to simulate selective grazing.
    The hyperspectral remote sensing variables that may be used to
    estimate the effect of species types, cultures and defoliation
    treatments were: the physiological reflectance index (PRI), the Carter
    index, R694, the ration of the Transformed Chlorophyll Absorption in
    Reflectance Index to the Optimized Soil-Adjusted Vegetation Index
    (TCARI/OSAVI) and the red-edge position. The PRI was found to be
    the most sensitive index. A significant increase (p < 0.001) in PRI
    was associated with the higher competitive ability of L. multiflorum
    than D. glomerata when the two were mixed. The response of the PRI
    from negative to positive over the measurement time in relation to
    height and dry matter yield suggest that the PRI may be used to
    study competitive ability because the related growth characteristics
    are indicators of competitive ability. This encourages further
    investigation of this method as a potential simpler and quicker
    alternative to the existing canopy height and pasture growth models.
    This may lead to efficient assessment and improved understanding of
    the condition and spatial patterns of forage vegetation species at field
    level.
    At field landscape level, using participatory GIS (PGIS), spatial
    knowledge on grazing intensity from pastoralists and local range
    ecology experts was elicited and relevant criteria generated and used
    to classify grazing intensity. Local pastoralists appeared to be more
    knowledgeable than local range ecology experts, possibly because of
    the pastoralists’ superior familiarity with the rangeland and better
    perceptions about the distribution of palatable species but the experts
    represented the grazing intensity better on a map. Local pastoralists
    have potential to contribute better to this process if the PGIS includes
    adequate training in the map making process. The local experts
    showed the capability to produce data and synthesize spatial
    variables, but it was also shown that the expert-based PGIS maps
    may not always be reliable. Using a proposition that “This area or
    pixel belongs to the high, medium, or low grazing intensity class
    because the local expert(s) says (say) so”, we tested for uncertainty
    in the PGIS-maps produced by different local experts using spatial
    tools such as evidential belief functions (EBFs).
    Evaluating the classification uncertainty in the different grazing
    intensity maps revealed that the maps with the lowest uncertainty
    were based on the composition of palatable vegetation species as the
    mapping criterion. This criterion may be used for mapping grazing
    intensity because it relates to measures of forage condition such as
    ground cover and quality, but it may be limited in use if other
    parameters such as vegetation composition and quantity are not
    integrated. If the definition of grazing intensity also includes these
    parameters and also livestock vegetation use factor and impacts on
    vegetation, then the proposition for EBF evaluation would be that:
    “This pixel or area is a specific grazing intensity class because of the
    level of livestock grazing use and its impacts on species composition,
    ground cover, quantity and quality. These parameters may be
    efficiently estimated using hyperspectral remote sensing. In order to
    include local knowledge in such an evaluation, research should
    establish how local pastoralists and experts may process the various
    parameters and how they may apply such a proposition.
    Since more than one criterion proved cumbersome for the local
    experts as evidenced by a weak correlation between the grazing
    intensity map and a grazing suitability index (r =0.35 (p < 0.01)),
    spatial multiple criteria tools may be useful for synthesizing the
    different mapping criteria.
    Overall, this study showed that high spectral resolution sensors can
    detect the effect of grazing and competitive interactions among
    forage plants through narrow band channels across the spectrum,
    while the local people perceive a few broad grazing intensity classes
    and spatially represent them using a few criteria. The two are
    complementary. The spectral sensor provides detailed information on
    the status and spatial patterns of vegetation, while local participants
    provide the spatial information on a more general coarse scale that
    may be used as baseline for hyperspectral remote sensing research.
    Effect van bladsnijregiem bij Anthurium andreanum op productie en kwaliteit
    Warmenhoven, M.G. ; Garcia Victoria, N. ; Mourik, N.M. van - \ 2005
    PPO BU Glastuinbouw (PPO nr. 41717068) - 13
    anthurium andraeanum - potplanten - bloementeelt - snoeien - ontbladering - cultuurmethoden - nederland - anthurium andraeanum - pot plants - floriculture - pruning - defoliation - cultural methods - netherlands
    Bladplukken in tomaat: Is meerproductie mogelijk door efficientere lichtbenutting?
    Kaarsemaker, R.C. ; Elgersma, R. ; Berkhout, B.A. ; Eunk, D. - \ 2005
    Naaldwijk : Praktijkonderzoek Plant & Omgeving B.V. (Rapport PPO ) - 32
    solanum lycopersicum - tomaten - snoeien - ontbladering - gebruiksefficiëntie - lichtrelaties - solanum lycopersicum - tomatoes - pruning - defoliation - use efficiency - light relations
    Licht is de basis voor de fotosynthese en de belangrijkste productiefactor voor een gewas. De optimale instelling van andere productiefactoren als bijvoorbeeld temperatuur en CO2-concentratie is vaak onderzocht, maar onderzoek naar de benutting van het licht in een volgroeid gewas in de praktijk heeft nooit veel aandacht gekregen. Er zijn veel proeven uitgevoerd met verschillende aantallen bladeren aan de stengel maar de lichtonderschepping in het gewas is bij de bladpluk proeven uit het verleden nooit gemeten. Wetenschappelijk is er wel veel onderzoek gedaan om de lichtonderschepping van een jong gewas met toenemend bladoppervlak modelmatig te beschrijven. Berekeningen met het opgestelde INTKAM model geven aan dat in de gangbare tomatenteelt onvoldoende licht wordt onderschept en extra lichtonderschepping meer productie op zou kunnen leveren.
    Roboter obernimmt die Handarbeit? Prototyp eines Automats fur den Gurkenbau entwickelt
    Henten, E.J. van; Hemming, J. ; Tuijl, B.A.J. van - \ 2005
    Gemüse 41 (2005)10. - ISSN 0016-6286 - p. 24 - 25.
    cucurbitaceae - cucumis sativus - komkommers - robots - plukken (picking) - mechanisch oogsten - ontbladering - automatisering - cucumbers - picking - mechanical harvesting - defoliation - automation
    Aan Wageningen Universiteit en Researchcentrum werd een robot ontwikkeld die komkommers kan oogsten en bladeren van planten kan verwijderen
    Leaf removal and prohexadione-calcium can modify Camarosa strawberry nursery plant morphology for plasticulture fruit production
    Reekie, J.Y. ; Hicklenton, P. ; Duval, J. ; Chandler, C. ; Struik, P.C. - \ 2005
    Canadian Journal of Plant Science 85 (2005)3. - ISSN 0008-4220 - p. 665 - 670.
    water-stress - growth - defoliation - conductance
    Mowing and the application of a new gibberellin biosynthesis inhibitor, prohexadione-calcium (ProCa), were studied as methods to modify the bate-root transplant morphology of Camarosa strawberry (Fragaria x ananassa Duchesne) in a Nova Scotia nursery. The effect these nursery practices had on fruit production in annual hill plasticulture was also determined. In one experiment Camarosa plants were sprayed with ProCa at an active ingredient concentration of 62.5 mg L-1 on Aug. 22, Sep. 05, or Sep. 19, 2001 and 2002, corresponding, respectively, to growing degree days (10 degrees C base) of 800, 894 and 965 in 2001 and 726, 821 and 908 in 2002. Application on Aug. 22 increased production of daughter plants, especially those of marketable size, by increasing the number of daughters per meter of runner and allocating more dry matter to marketable daughters. In a second experiment, field plots were mowed and/or treated with ProCa at an active ingredient concentration of 62.5 mg L-1 on Sep. 05 or Sep. 19, 2001 and 2002. All plants were dug in early October, shipped to Dover, Florida, and transplanted into plasticulture for fruit production. At digging, plants that had been mowed or treated with ProCa on Sep. 05 were reduced in plant height and total leaf area compared with untreated plants. Plants that were treated both with ProCa and mowed were the shortest. Fruit yield was higher from treated than from untreated plants. In 2001, the treatments increased early fruit production.
    Bladplukken bij paprika mogelijk rendabel
    Dueck, T.A. ; Marcelis, L.F.M. - \ 2005
    Groenten en Fruit. Algemeen 2005 (2005)28. - ISSN 0925-9694 - p. 16 - 17.
    capsicum - ontbladering - fotosynthese - energiegebruik - teelt onder bescherming - opbrengsten - paprika - glastuinbouw - capsicum - defoliation - photosynthesis - energy consumption - protected cultivation - yields - sweet peppers - greenhouse horticulture
    Plant Research International (PRI) onderzocht in welke mate de onderste bladeren van het gewas bijdragen aan de fotosynthese. Vervolgens is een inschatting gemaakt van de effecten op productie en energiegebruik
    Optimaal bladoppervlak levert geld op : voorzichtig zijn met teveel blad plukken bij tomaat
    Heuvelink, E. ; Kierkels, T. - \ 2005
    Onder Glas 2 (2005)2. - p. 14 - 15.
    tomaten - solanum lycopersicum - plantenontwikkeling - bladoppervlakte - bladoppervlakte-index - ontbladering - assimilatie - netto-assimilatiesnelheid - glastuinbouw - groenten - tomatoes - solanum lycopersicum - plant development - leaf area - leaf area index - defoliation - assimilation - net assimilation rate - greenhouse horticulture - vegetables
    Uit onderzoek blijkt dat sommige tomatentelers tot 10% meer licht weten te vangen dan andere telers. In principe betekent dat ook een 10% hogere productie. Het onderzoek bewijst: zorg voor een hoge lichtonderschepping door het gewas. Dat zorgt voor een optimale productie en optimale benutting van duur assimilatielicht. Gegevens in bijgaande grafiek: De hoeveelheid licht die het gewas onderschept loopt op naarmate het aantal vierkante meters blad per grondoppervlak groter is, tot een bepaalt maximum is bereikt
    Relationships between crown condition and its determining factors in the Netherlands for the period 1984 to 1994
    Hendriks, C.M.A. ; Olsthoorn, A.F.M. ; Klap, J.M. ; Goedhart, P.W. ; Oude Voshaar, J.H. ; Bleeker, A. ; Vries, F. de; Salm, C. van der; Voogd, J.C.H. ; Vries, W. de; Wijdeven, S.M.J. - \ 2000
    Wageningen : Alterra (Alterra-rapport 161) - 69
    kroon - bosbouw - ontbladering - verkleuring - stressfactoren - bosschade - monitoring - tijdreeksen - nederland - bosopstanden - crown - forestry - defoliation - discoloration - stress factors - forest damage - monitoring - time series - netherlands - forest stands
    From 1984 to 1994 forest condition in the Netherlands was estimated by recording defoliation and discolouration in 3000 plots. In this study the defoliation classes for this eleven years' period was related to possible stress factors such as deposition, soil chemistry and soil moisture. The data for most of the stress factors were derived using a site-specific model, since no measured data are available. The relationship was assessed by a split plot analysis. Results show that deposition and climaticstand, site and biotic factors contribute significantly to the explanation of defoliation, although percentages accounted for are low.
    On the relation between tillering, leaf area dynamics and growth of perennial ryegrass (Lolium perennne L.)
    Loo, E.N. van - \ 1993
    Agricultural University. Promotor(en): L. 't Mannetje; R. Rabbinge. - S.l. : Van Loo - ISBN 9789054851547 - 169
    polariteit - interacties - wortels - scheuten - lolium - ontbladering - polarity - interactions - roots - shoots - lolium - defoliation
    Modern intensively managed grasslands are subject to sward deterioration as a result of urine scorching, treading, winter mortality and late mowing or grazing. The major species in Dutch grasslands is perennial ryegrass. Deterioration consists of a decreasing presence of this species through death of tillers and plant. This gives rise to open swards which are subject to weed invasion and leads to a reduced productivity and nitrogen recovery. The objectives of this study were to increase the understanding of the recovery potential of open perennial ryegrass swards and of the relation between tiller density and herbage accumulation. Tiller production, tiller mortality, leaf area dynamics and growth as affected by cutting treatment, water availability, nitrogen supply and plant density were studied in field, glasshouse and phytotron experiments. The relative tiller appearance rate was studied as the product of leaf appearance rate and site filling. Leaf appearance rate was highly positively correlated with temperature and negatively with cutting height. Cutting frequency had no effect. Leaf appearance rate was reduced by low water potential and low nitrogen supply. Site filling decreased with decreasing nitrogen supply and increasing leaf area index. Just after defoliation, site filling was lower than later after defoliation, because of low substrate availability to developing tiller buds. In studying the effect of low and high nitrogen supply, genetic variation was found in nitrogen use efficiency. Populations with a high nitrogen use efficiency and a high herbage accumulation rate, also had a high leaf weight ratio and high tillering capacity. Models were developed for the simulation of changes in tiller number, leaf area expansion and dry matter accumulation of spaced plants and swards. These models were used for sensitivity analyses of the effect of leaf area expansion rate and leaf weight ratio on regrowth after defoliation and for the analysis of the importance of substrate availability for tillering and regrowth. The field experiments and the sward model showed that even with very low seeding rates, the amount of herbage harvested in the second harvest year is not lower than at very high seeding rates. Therefore, it was concluded that only when a low tiller density coincides with a clumped distribution of tillers and with a high frequency of patches without perennial ryegrass, reseeding of perennial ryegrass swards should be considered.
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